[GSoC] Functions: Corrects the _eval_as_leading_term() method of tan and sec functions

[sachin-4099]

Brief description of what is fixed or changed

This PR corrects the _eval_as_leading_term() method of tan and sec functions.

It also removes the check: if coeff is S.ComplexInfinity added in this PR: #19432, by handling the cases which returned zoo and correcting them.

Release Notes

• functions
  • Corrects the _eval_as_leading_term() method of tan and sec functions

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• functions
  • Corrects the _eval_as_leading_term() method of tan and sec functions (#19461 by @sachin-4099)

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#### Brief description of what is fixed or changed
This PR corrects the `_eval_as_leading_term()` method of `tan` and `sec` functions.

It also removes the check: `if coeff is S.ComplexInfinity` added in this PR: https://github.com/sympy/sympy/pull/19432, by handling the cases which returned `zoo` and correcting them.

#### Release Notes


<!-- BEGIN RELEASE NOTES -->
* functions
  * Corrects the `_eval_as_leading_term()` method of `tan` and `sec` functions
<!-- END RELEASE NOTES -->

Update

The release notes on the wiki have been updated.

[codecov]

Codecov Report

Merging #19461 into master will increase coverage by 0.008%.
The diff coverage is 100.000%.

@@              Coverage Diff              @@
##            master    #19461       +/-   ##
=============================================
+ Coverage   75.655%   75.663%   +0.008%     
=============================================
  Files          652       652               
  Lines       169727    169736        +9     
  Branches     40065     40065               
=============================================
+ Hits        128408    128429       +21     
+ Misses       35708     35703        -5     
+ Partials      5611      5604        -7     

[oscarbenjamin]

The exception handling in limits.py is a lot better. I'm not too familiar on the other parts of the codebase.

[sachin-4099]

The exception handling in limits.py is a lot better. I'm not too familiar on the other parts of the codebase.

Yeah, wanted a review from you regarding the exception handling part only.

[jksuom]

Looks good.